why does PHP json_encode ignore empty arrays?

Question

I have the following javascript that sends data to a PHP function:

<script>
    var mydata = {
                   id:123,
                   name: 'mike',
                   orders: []
    };

    $.ajax({
       type: 'POST',
       url:  'test.php',
       data: {save_data:mydata},
       success: function(data) {
                   alert('php received: ' + data);
       }
    });
</script>

and my test.php file contains the following code:

<?php
     if (isset($_POST['save_data'])) {
          $json = json_encode($_POST['save_data']);
          echo $json;     // just to check what has been received
          exit();
     }
?>

What I expect to received from PHP is: {"id":"123","name":"mike","orders":"[]"}

What I got back is {"id":"123","name":"mike"}

Notice that orders array has been eliminated from the output. No place holder for it. I tried adding some dummy elements in the array, and that worked fine, and I received the array back with the elements.

I need PHP to receive the json object as is, even if it contains empty arrays.

How can I do that?

instead of sending json data as url-encoded, you can set content-type as application/json and send the raw json. Then in php use can fetch the data using file_get_contents("php://input") — undefined_variable
– undefined_variable, Commented May 18, 2016 at 9:15
It's not php. Check actual request - there is not that empty array — vp_arth
– vp_arth, Commented May 18, 2016 at 9:27

Quentin · Accepted Answer · 2016-05-18 09:07:01Z

2

The JSON object is created inside PHP. Before then you just have form data.

jQuery will encode form data in a PHP-friendly style.

If you give it:

data: { foo: [1, 2, 3] }

It will convert that to:

foo[]=1&foo[]=2&foo[]=3

(although it will percent encode the [])

You get a key=value pair for each value.

If you have an empty array then you don't have any values, so you don't get any key=value pairs.

There is no way to encode "an empty array" using PHP's extensions to the form url encoding syntax.

You have two basic options:

Tell PHP about what data structure you want to create in advance and have it fill in the empty arrays.
Generate the JSON on the client

answered May 18, 2016 at 9:07

Quentin

949k136 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Ahmad Over a year ago

Will it work if I have a PHP class that matches the properties passed from json? if so, how can I tell PHP to instantiate an instance of the class using the values passed from the json?

Vo Kim Nguyen · Accepted Answer · 2016-05-18 09:18:29Z

0

It is not error of PHP. It cause by Jquery will igrone empty array when send it to server. So you have to parse array in 'orders' key to string JSON before send

var mydata = {
               id:123,
               name: 'mike',
               orders: []
};

Change to

var mydata = {
               id:123,
               name: 'mike',
               orders: JSON.stringify([])
};

answered May 18, 2016 at 9:18

Vo Kim Nguyen

1,65311 silver badges15 bronze badges

1 Comment

vp_arth Over a year ago

it will just "[]" string. You also need to parse this orderlist server-side.

Collectives™ on Stack Overflow

why does PHP json_encode ignore empty arrays?

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related